1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) device, and more particularly, to an organic light emitting diode (OLED) device with an improved color realization ratio.
2. Discussion of the Related Art
With the development of the information society, demands for various display devices increase. Accordingly, many efforts have been made to research and develop various flat display devices, such as liquid crystal display (LCD) devices, plasma display panels (PDP) and vacuum fluorescent display (VFD) devices, and some of them are already applied to displays of various equipment.
Among the flat display devices, organic light emitting diode (OLED) devices are self-luminous. Unlike LCD devices that can not emit light by themselves, OLED devices have no backlight unit because OLED devices are self-luminous display devices. In this respect, OLED devices can realize thin profile and lightweight. Also, OLED devices are suitable for mobile electronic equipment owing to the advantageous properties of high color purity, low power consumption and low driving voltage. In addition, OLED devices have rapid response speed and can be used in a wide temperature range. Especially, OLED devices can be manufactured at a low cost.
OLED devices have a fluorescent or phosphorescent organic-compound thin film. OLED devices emit light by the coupling of electrons and holes in the organic-compound thin film so that OLED devices realize a high picture quality and wide viewing angle as self-luminous devices.
A typical OLED device is provided with pixels arranged in a matrix to display images. Each pixel includes a light-emitting cell and a cell-driving part to drive the light-emitting cell independently. The light-emitting cell includes a pixel electrode connected with the cell-driving part, a common cathode connected with the ground, and a light-emitting part formed between the pixel electrode and the common cathode. The cell-driving part includes a gate line to which a scan signal is supplied, a data line to which a video data signal is supplied, a power-supplying line to which a common driving voltage is supplied, and two transistors and one storage capacitor connected between the data line and the power-supplying line.
An organic light-emitting diode (OLED) device according to the related art will now be described. FIG. 1 is a schematic view briefly illustrating an OLED device according to the related art.
The OLED device includes a substrate 16 having a metal layer 17, an organic light-emitting layer 14 formed on the metal layer 17, a transparent conductive layer 12 formed on the organic light-emitting layer 14, and a transparent substrate 10 formed on the transparent conductive layer 12. The metal layer 17 on the substrate 16 has a light-shielding function. Also, the light emitted from the organic light-emitting layer 14 progresses upward, and then passes through the transparent substrate 10, thereby representing colors. The organic light-emitting layer 14 includes a first organic light-emitting layer 14a to represent a red color, a second organic light-emitting layer 14b to represent a green color, and a third organic light-emitting layer 14c to represent a blue color.
In the case of an LCD device, white light is provided from a backlight unit positioned under an LCD panel, and some wavelengths of the white light are transmitted through a color filter layer of an upper substrate, whereby images are displayed on a screen. Meanwhile, the OLED device, as a self-luminous display device, directly emits red, green and blue lights from the organic light-emitting layers of the respective pixels, and the color purity of the lights are determined by the material characteristics of the light emitting layer of the pixels. In particular, the purity of the blue color is low compared to other colors in OLED devices.
Accordingly, the OLED device according to the related art has a problem of a low color realization ratio. In other words, the OLED device according to the related art may not represent all desired colors due to the low color purity of the lights generated from the organic light-emitting layers. Recently, continuous efforts are being made to display images with an improved color realization ratio.